The present invention relates to a mechanically controlled vacuum booster, in particular for brake systems of motor vehicles, comprising a pressure housing which can be fastened at one end wall to a carrier or support wall and at the other end wall to a force receiving device, such as a master brake cylinder. At least one movable wall is disposed in the pressure housing and a tube sealingly penetrates the movable wall and is connected to both end walls of the pressure housing. The movable wall subdivides the pressure housing into a low pressure or vacuum chamber and a working chamber and acts, via connecting elements projecting through slots in the tube and a reaction device, on a pressure bar disposed in the interior of the tube and extending to the force receiving device. A control housing subdivides the hollow chamber of the tube into two working chambers and the control housing contains a pressure controlling valve operated by a control bar which can be brought into operative connection with the reaction device.
A booster of this type is described in copending U.S. patent application Ser. No. 061,113, filed July 26, 1979, assigned to the same assignee as the present application, whose disclosure is incorporated herein by reference. This booster operates to boost the brake force in a motor vehicle and is activated by the difference in pressure between a vacuum produced by the motor and the atmospheric pressure. The importance of brake boosters of this type is in particular due to their considerably smaller weight with equal efficiency. This reduction in weight is achieved by the connection of the two end walls of the pressure housing by means of a central tube which receives the operating forces transmitted through the booster and applied to the central bar and part of the pressure forces acting the walls of the pressure housing, so that the pressure housing can have thin walls and a low weight. The saving of weight is, however, achieved by greater constructional expenditures, since additional sealings are necessary and additional means must be provided to transmit the boosting force produced at the movable wall to the pressure bar arranged in the interior of the tube.
In the brake booster according to the above-cited copending application cross elements, which can be fastened with screws, are provided at the movable wall to transmit the boosting force produced at the movable wall to the pressure bar. The cross elements project through slots in the tube and engage the grooves or clearances in the control housing. From the control housing the boosting force is transmitted to the pressure bar via a reaction device arranged in the control housing. This type of construction is relatively expensive and requires a great tube diameter.
From U.S. Pat. No. 3,102,453, issued Sept. 3, 1963, a brake booster is known, in which reaction levers are provided for the transmission of a reaction force to the control bar connected to the brake pedal. These levers have their outer end abutting against the movable wall, their inner end abutting against the control piston and their intermediate area abutting against the pressure bar. In this known brake booster the mounting of a tube to connect the end walls of the pressure housing is not disclosed.